1. Field of the Invention
The present invention relates to a rotation detection device that is used in various machines and equipments for detecting the angle of rotation and, in particular, for detecting the angle of rotation for the purpose of controlling the rotation of various motors, and also to a rotation detector equipped bearing assembly having such rotation detection device mounted therein.
2. Description of the Prior Art
In order to accurately detect the status of rotation of a rotary body used in, for example, an automotive vehicle or a railway vehicle, a desire has often arisen to detect a rotation signal with high resolving power and high precision. In a wheel support bearing assembly for rotatably supporting a vehicle wheel relative to a vehicle body structure, an ABS sensor is employed for the control of an anti-lock brake system, that is, for the ABS control. This ABS sensor in the state of art has a not-so-high revolving power. If with such a sensor the rotation can be detected with high resolving power, it is possible to utilize that for a high degree vehicle control such as, for example, automated drive, assisted drive, safety control and so on in the future. Also, in the control of a motor, accurate detection of the rotational position of the rotor is required for the purpose of achieving a high efficiency, noise reduction and reduction of torque ripples and such accurate rotational position can be utilized for a high level control of operation.
A rotation detection device of this kind has been suggested, which includes a first encoder, having a main track and a revolution pip track, and a second encoder used to detect the phase in a rotor of a motor and is so designed that based on a detection signal from sensors disposed in face-to-face relation with those encoders, a train of signals necessary for the motor control can be generated. (See, for example, the Patent Document 1 listed below.)
A rotation detection device utilizing a winding stator and a rotor has also been suggested, in which an absolute encoder is provided by forming a plurality of tracks having different numbers of magnetic poles in the rotor so that the absolute rotation angle can be detected based on the difference in phase between signals detected from the tracks. (See, for example, the Patent Document 2 listed below.)
A rotation detection device has further been suggested, in which a plurality of magnets arranged in a direction circumferentially of an outer periphery of a rotor and a plurality of magnetic sensors provided in an inner periphery of a stator and positioned at different locations in the direction circumferentially thereof are combined together so that the absolute angle can be detected by calculating the output signals generated from those magnetic sensors. (See, for example, the Patent Document 3 listed below.)
A still further rotation detection device has been suggested, which includes a ring-shaped magnetic pulse generating means such as, for example, a magnetic encoder having magnetic pole pairs in a direction circumferentially thereof and for generating magnetic pulses, and a plurality of detecting elements for detecting the magnetic pulses, substantially aligned in a direction circumferentially thereof and associated with the magnetic pulse generating means and is so designed that the absolute angle can be detected by calculating the respective output signals generated from the detecting elements. (See, for example, the Patent Document 4 listed below.)    [Patent Document 1] JP Laid-open Patent Publication No. 2004-271503    [Patent Document 2] JP Laid-open Patent Publication No. 2006-322927    [Patent Document 3] JP Laid-open Patent Publication No. 2006-525518    [Patent Document 4] JP Laid-open Patent Publication No. 2002-541485
However, the rotation detection devices of the structure discussed hereinabove have the following problems.                While a resolver is currently largely employed for the detection of rotational position of, for example, a motor, there is a problem that the manufacturing cost is high.        In each of the rotation detection devices of the structure discussed hereinabove, the type in which a magnetic encoder is employed has a difficulty in detecting the absolute angle and, also, securing rotation pulses with high resolving power.        In the case of the rotation detection device disclosed in the Patent Document 1, the structure is complicated and also the absolute angle cannot be detected in a non-rotating condition.        The rotation detection device disclosed in the Patent Document 2 is of a system similar to that employing the resolver and is an example in which influence brought about by misalignment relative to the rotor is reduced, but there is a problem that a complex coil is needed.        In the case of the rotation detection device disclosed in the Patent Document 3 and designed to detect the rotation of magnets with magnetic sensors, although the angle of rotation can be detected, the intensity of the magnetic field must be detected with high precision and the detection gap must be controlled accurately in order to determine the angle of rotation with high precision. Also, in order to allow this system to output rotation pulse signals, a processing circuit is needed for generating pulse signals based on the angle detected.        
An object of the present invention is to provide a rotation detection device which is simple in structure and capable of accurately detecting the rotational position of a rotary body and in which the manufacturing cost can be reduced by simplifying assemblage and processing thereof and, also, a rotation detection device equipped bearing assembly having such rotation detection device mounted therein.